There are widely known homotransplants for layer-by-layer keratoplasty in the form of fresh and preserved cornea (cf "Optical Transplantation of Cornea and Tissue Therapy" by V. P. Filatov, in Russian, Moscow, 1945; "Transplantation of Cornea at Complicated Leukoma" by N. A. Puchkovskaya, in Russian, Kiev, 1960).
However, broad introduction of this surgical operation into clinical practice is significantly complicated by difficulties concerned with uninterrupted supply of cadaver eyes to clinics. The ethical considerations of borrowing the eyes from cadavers more often than not are in the way of obtaining the material and providing the stock of preserved cornea. Such difficulties are all but unsurpassable in numerous countries of Asia, America and Africa, stemming as they are from strong national and religious traditions (cf. "Keratoplasty" by R. Paton, New York, 1955).
Moreover, the transplanted cornea in numerous cases displays the tendency to opacify, which means the failure of the conducted operation (cf. the abovecited "Transplantation of Cornea at Complicated Leukoma" by N. A. Puchkovskaya). When keratoplasty is resorted to as the treatment of vascular leukoma and hyperplastic processes of the conjunctiva, cornea homotransplants more often than not become vascularized, which brings about their opacification, and also a recurrence of the disease.
There are also known thinnest transparent films prepared from either fermentation-depolymerized or dispersion-purified skin collagen, or else from cattle tendon, which have been used as heterotransplants for layer-by-layer keratoplasty exclusively in experimental studies and failed to be accepted in the clinical practice (cf. "Collagen-Derived Membrane: Corneal Implantation" by M. N. Dunn et al., Am. Journal of Ophthalmology, 1967, Vol. 157, No. 15, pp. 1329-1330; "Lamellar Keratoplasty: Use of a Collagen Graft for Corneal Replacement" by J. Tanner et al., Eye, Ear, Nose Therapy Monthly, 1968, Vol. 7, No. 8, pp. 368-372). The process of preparing such films is both complicated and costly, and can be conducted exclusively under industrial conditions.
There is also known from literature (cf. J. Malbran in Archives of Soc. Ophthal. Hisp. Am., 1954, Vol. 14, p. 1167) the use of tendons as the homoplasty material for some ophthalmological operations (with the sclera and lids). However, there have been no data available on the use of tendons for plasty of such highly differentiated tissue of the eye as the cornea.
Thus, the hitherto known transplants used for layer-by-layer or lamellar keratoplasty fail to satisfy the demands of the countries that need them. This can be vividly perceived from an analysis of ophthalmological diseases in different nations. Thus, according to the data available from the World Health Organization (WHO) - cf. Chronicle of WHO, 1979, Vol. 1, No. 1 - there are 40 million people in the world suffering from trachoma, and in 6 million cases this disease had resulted in blindness. The highly developed nations of Europe and America likewise have a considerable demand for the plasty material, their blindness index being within the range from 0.2 to 0.7%. In the USA alone (blindness index 0.2%) blindness was caused in 4.7% of the cases by various lesions of the cornea and conjunctiva. In real figures, this percentage means dozens of thousands of humans requiring layer-by-layer keratoplasty.